1. Field of the Invention
The present invention relates to an apparatus provided with a carriage. More particularly, the invention relates to the arrangement of a guide member when the carriage moves.
2. Related Background Art
Conventionally, it has been practiced for a recording apparatus, such as a printer or facsimile equipment, that records images on a recording sheet or some other recording medium in accordance with recording information or a reading apparatus that reads images from a source document, to mount a recording head or a reading head on a carriage capable of reciprocating along the guide member, such as a guide shaft, provided for the apparatus main body, and to perform recording or reading of information by driving the carriage to scan the surface of various kinds of media, such as a recording medium or a source document. Here, usually, two or more guide members (guide shafts or the like) guide and support a carriage to enable it to reciprocate.
The serial type recording apparatus serving as an apparatus provided with a carriage, which mounts a recording head that functions as recording means, performs reciprocal scanning for the execution of recording on a recording medium by driving the recording head to move in accordance with the recording signal and scanning, which are arranged to be in synchronism with each other. In recent years, along with more demand in obtaining images in higher precision, it is required for the scanning by use of a carriage to be more stable and executable at a speed made more constant then ever.
The carriage speed fluctuates often due to the fluctuation of rotational speed of a motor serving as the driving source, the eccentricity of gears or pulleys used for transmitting driving power, the backlash of toothed timing belt or gear used for transmission of the driving power, and the overshooting after the acceleration of the carriage, among some other driving means or driving transmitting means. Various studies are being made in order to reduce them.
On the other hand, not only by the speed fluctuation in the direction of the parallel advancement of the carriage, but also, by fine posture changes of the carriage (due to swinging or vibration), the recorded images may be disturbed in some cases.
Generally, the carriage is guided and supported in such a manner that a column (or cylindrical) guide shaft, having a slightly smaller diameter than the diameter of the circular hole of a bearing portion integrally arranged for the carriage, is penetrated through the hole thus arranged, and that the other portion of the carriage is allowed to abut against the guide rail arranged to extend substantially in parallel with the guide shaft. Also, in order to hold the carriage stably in the scanning direction, the bearing portion is arranged in plural locations apart from each other (usually in two locations) in the carriage scanning direction. At this juncture, the outer diameter of the guide shaft is made slightly smaller than the inner diameter of the bearing portion so that the carriage can slidably move smoothly along the guide shaft through the bearing portions arranged in plural locations. As a result, there exists a slight clearance (play) between the guide shaft and the bearing portion.
In this respect, it is desirable to provide driving means for the one of two guide members (the aforesaid guide shaft and guide rail), which has a larger sliding load. Usually, therefore, the carriage driving motor is connected near the bearing portion to be able to transmit the driving power.
During scanning of the carriage, should there exist obstacles, such as scratches or dust particles, on the guide rail, for example, the carriage slows down due to resistance on the sliding portion of the rail, and moment occurs on the bearing portion in the advancing direction. As a result, the carriage tends to rotate (or swing) in that direction. Then, the carriage rotates minutely due to the play between the outer circumferential surface of the guide shaft and the inner diameter of the bearing portion, and, further, the rotational motion in the opposite direction occurs due to repulsion exerted by the guide shaft. Consequently, a problem is encountered that the carriage vibrates.
Also, when the carriage begins scanning, the carriage accelerates by the addition of the driving power from driving means (the carriage motor). However, since the gravitational center of the carriage is usually placed near the central portion thereof so that it is away from the position near the bearing portion having the driving means connected therewith (the acting point of driving power), the carriage tends to rotate around the gravitational center instantaneously due to the inertia of its own. Such minute rotation (or swinging) as this also presents the problem that the carriage is caused to vibrate as described earlier.
In order to solve these problems, it is generally practiced to use the oil-immersed bronze member formed by sintered material for the bearing portion that fits with the guide shaft so as to enhance the precision of the bearing portion. However, for a structure such as this, the sintered material must be fixed to the carriage in good precision by the insert formation, bonding, or the like. Then, there is a problem that this arrangement leads to increasing costs. Also, with the installation of the bearing portion formed by sintered material, the carriage should be made larger to present a problem that the apparatus main body is made larger inevitably. Further, even with the adoption of a structure using sintered material, it is impossible to eliminate the play between the guide shaft and the bearing portion completely. Then, a problem is encountered that there is naturally a limit to the effect that may be produced on the reduction of vibration (or swinging) of the carriage in this way.
Meanwhile, there has been proposed in the specification of Japanese Patent Application Laid-Open No. 07-19246, a method for suppressing the swinging of the guide shaft inside the bearing portion with the provision of two flat surfaces above the bearing portion, each facing the guide shaft, respectively, to enable the guide shaft to be depressed to these two faces. In order to allow the two bearing flat surfaces that face the guide shaft to abut against it equally and stably by use of this method, the weight of the carriage itself should be large to a certain extent, and also, there is a need for arranging the guide rail to be away from the guide shaft as much as possible in the direction substantially perpendicular thereto.
A method of the kind, however, is inadequate for a serial type apparatus, such as a small recording apparatus for which the weight of carriage is made smaller, and the dimension in the height direction is also made smaller. There is a possibility that more vibration takes place during carriage scanning, and there remain technical problems yet to be solved.